There have been known multi-layer piezoelectric elements which are used in the fuel injection apparatus of automobile engine or the like. FIG. 13(a) is a perspective view showing a multi-layer piezoelectric element of the prior art. The multi-layer piezoelectric element 101 comprises a stack 109, consisting of a plurality of piezoelectric layers 105 and a plurality of internal electrode layers (metal layers) 107, the piezoelectric layers 105 and the internal electrode layers 107 being stacked alternately one on another, and a pair of external electrodes 111 formed on the side faces of the stack 109.
The internal electrode layers 107 are not formed over the entire principal surfaces of the piezoelectric layers 105, but have the so-called partial electrode structure. FIG. 13(b) is an exploded perspective view of a part of the multi-layer piezoelectric element 101 shown in FIG. 13(a) explanatory of the partial electrode structure. As shown in FIG. 13(a) and FIG. 13(b), the internal electrode layers 107 are stacked in a staggered manner so as to be exposed alternately on the left side face of the stack 109 in one layer and then on the right side face of the stack 109 in the next layer. With this constitution, the plurality of internal electrode layers 107 are electrically connected to a pair of the external electrodes 105 in every other layer. Inactive layers 113, 113 are stacked on both end faces of the stack 109 in the direction of stacking.